A NOVEL KIND OF SOLID ROCKET PROPELLANT

Cryogenic Solid Propellants (CSPs) combine the simplicity of conventio nal solid propulsion with the high performance of liquid propulsion. B y introducing materials that require cooling for remaining solid, CSPs offer an almost unlimited choice of propellant constituents that migh t be selected with respect to specific impulse, density or environment al protection. The prize to be paid for these advantages is the necess ity of constant cooling and the requirement of special design features that provide combustion control by moving from deflagration to hybrid -like boundary layer combustion. This is achieved by building the soli d propellant grains out of macroscopic elements rather than using the quasi homogeneous mixture of conventional composites. The elements may be coated, providing protection and support. Different elements may b e designed for individual tasks and serve as modules for ignition, sus tained combustion, gas generation, combustion efficiency enhancement, etc. Modular dissected grains offer many new ways of interaction insid e the combustion chamber and new degrees of freedom for the designer o f such ''multiple internal hybrid grains''. At a preliminary level, a study finished in Germany 1997 demonstrated large payload gains when t he US Space Shuttle and the ARIANE 5 boosters were replaced by CSP-boo sters. A very preliminary cost analysis [5] resulted in development co sts in the usual magnitude (but not in higher ones). Costs of operatio n were identified as crucial, but not established. Some experimental w ork in Germany is scheduled to begin in 1998. However, almost all deta ils in this article (and many more that were not mentioned - most prom inent cost analyses of CSP-development and operations) wait for deeper analysis and verification. Actually, a whole new world of chemical pr opulsion awaits exploration. The topic can be looked up and discussed at the web site of the Advanced Propulsion Workshop of the Internation al Academy of Astronautics. The author would be pleased to provide the necessary access data. (C) Elsevier, Paris.